The present disclosure provides protease-resistant peptides, methods of making such peptides, as well as compositions comprising protease-resistant peptides and methods of treatment utilizing such peptides. Lipid modification of amino acids at certain positions in the peptide sequence is described herein.
The development of long-acting peptide therapeutics is hampered by factors such as short plasma half-life and poor oral bioavailability, largely a result of the natural susceptibility of peptides to enzymatic degradation. The majority of proteolytic functions are necessary, including regulating essential biomolecular processes such as turning off peptide signaling events at cell surfaces, or the gastric breakdown of proteins and peptides during digestion. Thus, the activity of the responsible proteases cannot simply be inhibited without, in many cases, causing other metabolic disturbances.
In order to overcome degradation, increasing the enzymatic resistance of a peptide of interest is therefore desirable. Generally, two methods are utilized to increase enzymatic resistance: sequence specific modifications, e.g., those affecting the primary structure of the peptide itself; and globally effective modifications, e.g., those which alter certain overall physicochemical characteristics of the peptide. Introduced strategically, such modifications can reduce the effects of natural physiological processes which would otherwise eliminate or inactivate a peptide whose action is desired, e.g. enzymatic degradation and/or clearance by renal ultrafiltration.
Sequence specific modifications include incorporation of proteolysis-resistant unusual amino acids, or more involved modifications including cyclization between naturally occurring side-chain functions, e.g. disulfide formation (Cys-Cys), or lactamization (Lys-Glu or Lys-Asp). Additional modifications include cyclization between unnatural amino acid surrogates within the peptide backbone e.g. olefin metathesis stapling.
Global modifications include processes such as peptide lipidation e.g. palmitoylation and/or PEGylation. Palmitoylation has the effect of creating a circulating reservoir of peptide which reversibly associates with naturally abundant albumin in blood serum. Peptide associated with albumin effectively escapes renal ultrafiltration since the size of the associated complex is above the glomerular filtration cutoff. As the peptide dissociates from the surface of the albumin it is again free to interact with endogenous receptors. PEGylation has the effect of physically shielding the peptide from proteolysis and imparts significant hydrophilicity which upon hydration greatly increases the hydrodynamic radius of the therapeutic molecule to overcome renal clearance.
While these technologies can be broadly applicable to therapeutic peptides in general, and to an extent are able to extend circulatory half-life, a need still exists for methods of increasing stability of peptides and proteins to enzymatic degradation, particularly in light of the desire to produce peptides suitable for oral administration.